1. Field of the Invention
The present invention relates to an induction heating coil assembly used for heating the inner wall of a cylindrical member to form a plurality of separate partial hardened layers circumferentially therein, and relates to a method for hardening the inner wall of a cylinder, in particular, the inner wall of a cylinder block, by using the induction heating coil.
2. Description of Related Art
Conventionally, "an induction heating coil assembly" used for hardening the entirety of the circumference of the inner wall of a cylindrical member to be heated is disclosed in Japanese Laid-Open Patent Publication No. Sho 58-73990 which was previously filed in Japanese Patent Office by the applicant.
The above conventional induction heating coil assembly comprises a plurality of wound conductive parts which are concentrically provided at equal spaces in the cylindrical member to be heated having a small diameter, in order concentrically to form a plurality of ring-shaped hardened layers which are vertically arranged, in the inner wall of the cylindrical member. The adjacent winded conductive parts of the induction heating coil assembly have winding directions reverse to each other. A core made of a magnetic substance is attached to each winded conductive part in order to concentrate alternative magnetic flux generated by each winded conductive part to only a predetermined area of the circumferential wall of the cylindrical member to be heated which is opposed to each winded conductive part.
Therefore, the hardening treatment using such an induction heating coil assembly forms a plurality of circumferential ring-shaped hardened layers in the inner wall of a cylindrical member to be heated having a small diameter, so that strain which was produced by a conventional method for hardening the entirety of the circumference of the inner wall is not produced in the inner wall. Thereby, an abrasion resistance is given to a predetermined inner wall of the cylindrical member with a small diameter.
However, as mentioned above, the conventional induction heating coil assembly has a complicated construction. Therefore, there is a problem that such a conventional induction heating coil assembly and such a conventional method for hardening the inner wall of a cylinder require large manufacturing costs.
The induction heating coil having such a construction can be utilized for only the purpose of forming a plurality of circumferential continuous ring-shaped hardened layers arranged vertically at equal spaces in the inner wall of a cylindrical member to be heated which has a small or large diameter. Therefore, there is another problem that such an induction heating coil assembly or the method for hardening an inner wall of a cylinder using such an induction heating coil assembly cannot respond to a requirement of dividing each circumferential portion to be heated of the inner wall of the cylindrical member into plural separate parts at desired positions and to a requirement of heat-treating collectively to form a plurality of separate partial hardened layers on a line of a circumferential ring on the inner wall.
Since the conventional induction heating coil assembly comprises a plurality of winded conductive parts, the induction heating coil assembly and the conventional method using such an induction heating coil assembly require a large electric power and it is difficult to control the electric power supplied to each winded conductive part constantly.